This paper presents the results of an experiment, conducted on-board the Russian MIR Space Station during a joint Russian and European mission, EUROMIR '94. A commercially available IBM ThinkPad 750C was evaluated by running a software system which monitored the notebook's behaviour and counted the number of single event upsets. The used software system and ground verification tests are also presented. Finally, another software system, able to ruggedize normal personal computers for usage in space, is described.